The number of hate crimes committed in Moscow has exploded this year, rising sixfold compared to the same period last year, Investigative Committee head Alexander Bastrykin said Friday.

The authorities registered 73 hate crimes in Moscow in the first six months of this year, a trend Bastrykin said must be halted with "decisive and systematic efforts."

"We are worried that while the overall number of crimes registered in Russia has shrunk by 9 percent, crimes of an extremist nature are increasing year after year," Bastrykin said, Interfax reported.

The Moscow branch of the Investigative Committee announced Friday that it had opened two criminal cases involving hate crimes, one of which involves 12 racially motivated murders.

The announcement came after the beginning of two high-profile trials in the Moscow City Court last week, in which several teenagers are accused of murdering multiple dark-skinned victims — as well as an Investigative Committee statement Thursday saying seven ultranationalists are suspected in at least 21 racially motivated murders.

Mikhail Ionkin, spokesman for the committee's Moscow branch, said the spike in hate crimes was not just a reflection of the authorities' efforts to crack down on such crimes.

"It's no secret that hate crimes are on the rise," Ionkin said. "We are not registering more because of any change in methods or priorities on our part. We have always worked with equal focus against extremism."

Ionkin declined to say what could be behind the dramatic rise. "It's complicated," he said.

The case of Artur Ryno, who went on trial last week in the Moscow City Court with eight other people suspected of committing 20 racist murders, received so much publicity that it could have sparked copycat crimes, said Galina Kozhevnikova, deputy head of the Sova center, which tracks hate crimes.

But the authorities' apparent decision to prosecute neo-Nazi groups more actively could also be contributing to the spike, Kozhevnikova said.

"In big cities, we know there are lots of underground Nazi groups," she said. "When the government began to investigate their activities and arrest them, they reacted violently against ethnic minorities."

Kozhevnikova cited an incident earlier in the year when a racist murder was committed in the same location where a group of neo-Nazis had been arrested by police in Moscow the previous day.

A city police spokesman denied Friday, however, that there has been any rise in hate crimes in the city this year.

"Such crimes are becoming less frequent," said the spokesman, who declined to give his name. "In my opinion, certain organizations beef up the statistics on such crimes in order to attract funding."

The Sova center recorded 60 racist murders across the country so far this year, while it recorded a total of 85 such crimes in all of 2007. The actually number of hate crimes is likely three to four times higher than the number registered by authorities, Kozhevnikova said.